Posterior stabilization systems and methods

ABSTRACT

Various methods and devices for repairing and/or restoring function to a damaged, injured, diseased, or otherwise unhealthy facet joint, lamina, posterior ligament, and/or other features of a patient&#39;s spinal column are provided. In an exemplary embodiment, the methods and devices are effective to mimic the natural function of the posterior elements, preferably without necessarily mimicking the anatomy, by allowing a high degree of flexibility between two adjacent vertebrae when the vertebrae are moved within a first range of motion, and by controlling movement of the adjacent vertebrae within a second range of motion beyond the first range of motion.

FIELD OF THE INVENTION

The present invention relates to spinal instrumentation, and in particular to various devices that are adapted to mimic the natural function of the structural posterior elements.

BACKGROUND OF THE INVENTION

The vertebrae in a patient's spinal column are linked to one another by the disc and the facet joints, which control movement of the vertebrae relative to one another. Each vertebra has a pair of articulating surfaces located on the left side, and a pair of articulating surfaces located on the right side, and each pair includes a superior articular surface, which faces upward, and an inferior articular surface, which faces downward. Together the superior and inferior articular surfaces of adjacent vertebra form a facet joint. Facet joints are synovial joints, which means that each joint is surrounded by a capsule of connective tissue and produces a fluid to nourish and lubricate the joint. The joint surfaces are coated with cartilage allowing the joints to move or articulate relative to one another.

Diseased, degenerated, impaired, or otherwise painful facet joints and/or discs can require surgery to restore function to the three joint complex. Subsequent surgery may also be required after a laminectomy, as a laminectomy predisposes the patient to instability and may lead to post-laminectomy kyphosis (abnormal forward curvature of the spine), pain, and neurological dysfunction. Damaged, diseased levels in the spine were traditionally fused to one another. While such a technique may relieve pain, it effectively prevents motion between at least two vertebrae. As a result, additional stress may be applied to the adjoining levels, thereby potentially leading to further damage.

More recently, techniques have been developed to restore normal function to the facet joints. One such technique involves covering the facet joint with a cap to preserve the bony and articular structure. Capping techniques, however, are limited in use as they will not remove the source of the pain in osteoarthritic joints. Caps are also disadvantageous as they must be available in a variety of sizes and shapes to accommodate the wide variability in the anatomical morphology of the facets. Caps also have a tendency to loosen over time, potentially resulting in additional damage to the joint and/or the bone support structure containing the cap.

Other techniques for restoring the normal function to the posterior element involve arch replacement, in which superior and inferior prosthetic arches are implanted to extend across the vertebra typically between the spinous process. The arches can articulate relative to one another to replace the articulating function of the facet joints. While these techniques can be effective in replacing the bony elements, they do not specify a means to replace the function of the soft tissues and more specifically a means to mimic the load deformation curve of the natural spine.

Accordingly, there remains a need for improved systems and methods that are adapted to mimic the natural function of the facet joints.

SUMMARY OF THE INVENTION

The present invention provides various methods and devices for repairing and/or replacing a damaged facet joint, and optionally for replacing other posterior elements, including, for example, the lamina, the posterior ligaments, and/or other features of a patient's spinal column. In one exemplary embodiment, an implantable device for replacing and/or stabilizing one or more facet joints in a patient's spinal column is provided and it generally includes at least one dynamic stabilizing member, e.g., a flexible member, and at least one stabilizing rod or connector that is adapted to couple to adjacent vertebrae and that is adapted to extend through the at least one flexible member. In an exemplary embodiment, the device includes superior and inferior connector members that are adapted to mate to superior and inferior vertebrae, respectively, and the flexible member(s) is adapted to span across at least two adjacent vertebrae in a patient's spinal column. In use, the superior and inferior connectors and the flexible member(s) are effective to control movement between the superior and inferior vertebrae. More preferably, the connector(s) are adapted to slidably and/or rotatably move relative to the flexible member(s), preferably without deforming the flexible member(s), when the adjacent vertebrae are moved within a first range of motion, and they are preferably adapted to deform the flexible member(s) when the adjacent vertebrae are moved within a second range of motion beyond the first range of motion.

The flexible member(s) can have a variety of configurations, shapes, and sizes. In one embodiment, the implant includes two flexible members and each flexible member has a substantially elongate shape. The flexible members can also have a shape that is in the form of an hour-glass. In another embodiment, the implant can include a single flexible member, and the flexible member can optionally have a shape that is substantially in the form of an hour-glass. The flexible member(s) can also have an elasticity that varies. For example, the flexible member can have a central portion that has an elasticity that is greater than an elasticity of opposed superior and inferior terminal ends thereof. In another embodiment, each flexible member can include at least two thru-bores formed therein for receiving the superior and inferior connectors therethrough. Each thru-bore can include a bushing or bearing disposed therein and adapted to receive a connector. The region surrounding the thru-bores can have properties or characteristics that vary, or that are at least different than the properties of the central region. In one embodiment, a region surrounding each thru-bore is adapted to provide stability to the connector extending therethrough. As such, each region surrounding the thru-bores can be substantially rigid or have less elasticity than the central portion.

Each connector can also have a variety of configurations, and in one embodiment each connector is in the form of a substantially rigid rod. More preferably, the superior connector includes opposed terminal ends that are adapted to couple to the pedicles of the superior vertebra, and a mid-portion that is adapted to extend around and be positioned inferior to the spinous process of the superior vertebra, and the inferior connector includes opposed terminal ends that are adapted to couple to the pedicles of the inferior vertebra, and a mid-portion that is adapted to be positioned proximate and superior to the spinous process of the inferior vertebra. In an exemplary embodiment, the superior connector is substantially v-shaped and the inferior connector is generally linear with a v-shaped portion formed therein. More preferably, the v-shaped superior connector includes a central linear portion and first and second lateral arms extending at an angle relative to the central linear portion, and the v-shaped portion in the inferior connector is preferably formed at a substantial mid-point thereof. In use, the v-shaped portion of the inferior connector can be adapted to fit around the spinous process of the inferior vertebra, and the v-shaped superior connector can be adapted to extend around the spinous process of the superior vertebra. Each connector can also include first and second terminal ends that are adapted to be fixedly mated to opposed sides of a vertebra. By way of non-limiting example, a spinal anchor, such as a spinal screw, can be used to fixedly a terminal end of a connector to the vertebra.

The present invention also provides methods for replacing and/or stabilizing the posterior elements in adjacent vertebrae. In one embodiment, the method can include the steps of coupling at least one flexible member to two adjacent vertebrae with at least one connector such that the at least one connector is slidably and/or rotatably movable relative to the at least one flexible member, preferably without substantially deforming the flexible member, when the vertebrae are moved within a first range of motion, and such that the at least one connector is effective to stretch and/or deform the at least one flexible member when the vertebrae are moved within a second range of motion beyond the first range of motion. Preferably, the step of coupling at least flexible member to two adjacent vertebrae with at least one connector comprises coupling a superior connector to a superior vertebra, and coupling an inferior connector to an inferior vertebra. The superior connector and the inferior connector can extend through first and second flexible members. In one embodiment, the superior and inferior connectors can be coupled to the superior and inferior vertebrae, respectively, by implanting first and second spinal anchors in each of the superior and inferior vertebra and locking the superior and inferior connectors to the spinal anchors.

In yet another embodiment, a method for restoring normal function to the posterior elements and/or replacing the posterior elements of adjacent vertebrae in a patient's spinal column is provided and it includes the steps of implanting a first pair of spinal anchors in opposed pedicles of a first vertebra, implanting a second pair of spinal anchors in opposed pedicles of an adjacent second vertebra, coupling opposed terminal ends of a first rigid member to the first pair of spinal anchors in the first vertebra, and coupling opposed terminal ends of a second rigid member to the second pair of spinal anchors in the second vertebra. The first and second rigid members preferably extend through at least one flexible member. In an exemplary embodiment, the first and second rigid members extend through first and second flexible members that are preferably positioned on opposed sides of a spinous process of each vertebra.

The method can also include the step of implanting a third pair of spinal anchors in opposed pedicles of a third vertebra adjacent to the second vertebra, coupling opposed terminal ends of a third rigid member to the second pair of spinal anchors in the second vertebra, and coupling opposed terminal ends of a fourth rigid member to the third pair of spinal anchors in the third vertebra. The third and fourth rigid members preferably extend through the at least one flexible member.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be more fully understood from the following detailed description taken in conjunction with the accompanying drawings, in which:

FIG. 1A is a perspective view illustration of two adjacent vertebrae coupled to one another by a facet joint stabilizing device in accordance with one embodiment of the present invention;

FIG. 1B is a side view illustration of the vertebrae and device shown in FIG. 1A;

FIG. 1C is a front view illustration of the vertebrae and device shown in FIG. 1A;

FIG. 2A is a side view illustration of the superior connector of the device shown in FIGS. 1A-1C;

FIG. 2B is a side view illustration of the inferior connector of the device shown in FIGS. 1A-1C;

FIG. 2C is an exploded view illustration of one of the flexible members of the device shown in FIGS. 1A-1C;

FIG. 2D illustrates another embodiment of a posterior element stabilizing device having hour-glass shaped flexible members;

FIG. 3 is a chart showing a typical load-deformation curve of a human functional spine unit; and

FIG. 4 is a perspective view of another embodiment of a posterior element stabilizing device in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides various methods and devices for replacing damaged, injured, diseased, or otherwise unhealthy posterior elements, such as the facet joints, the lamina, the posterior ligaments, and/or other features of a patient's spinal column. In an exemplary embodiment, the methods and devices are effective to mimic the natural function of the spine by allowing a high degree of flexibility between two adjacent vertebrae when the vertebrae are moved within a first range of motion, and by controlling or limiting movement of the adjacent vertebrae within a second range of motion beyond the first range of motion. A person skilled in the art will appreciate that, while the methods and devices are especially configured for use in restoring and/or replacing the facet joints and optionally other posterior elements of a patient's spine, the methods and devices can be used for a variety of other purposes in a variety of other surgical procedures.

FIGS. 1A-1C illustrate one exemplary embodiment of a posterior element replacement implant connected between adjacent vertebrae 60, 62. As shown, the implant 10 generally includes first and second flexible members 12, 14, also referred to as dynamic stabilizing elements, and first and second connectors 16, 18, also referred to as stabilizing rods. The implant 10 is preferably effective to mimic the natural function of the spine. As shown in FIGS. 1A-1C, the implant 10 is coupled to superior and inferior vertebrae 60, 62 such that it is effective to perform the function of the posterior elements that connect the vertebrae, or to otherwise control movement of the vertebrae 60, 62. More particularly, the first connector 16, hereinafter referred to as the superior connector 16, is coupled to the superior vertebra 60, and the second connector 18, hereinafter referred to as the inferior connector 18, is coupled to the inferior vertebra 62. The superior and inferior connectors 16, 18 extend through the first and second flexible members 12, 14, such that the connectors 16, 18 are coupled to one another via the flexible members 12, 14. As a result, the connectors 16, 18 and the flexible members 12, 14 are effective to control movement of the vertebrae 60, 62 relative to one another, thereby functioning in place of the posterior elements. In an exemplary embodiment, the flexible members 12, 14 are movable, e.g., rotatable and/or slidable, but preferably not deformable, relative to at least one of the connectors, e.g., the superior connector 16, when the vertebrae 60, 62 are moved within a first range of motion, and at least one of the connectors, e.g., the superior connector 16, is effective to deform, e.g., stretch, rotate, etc., the flexible members 12, 14, or otherwise create resistance, when the superior and inferior vertebrae 60, 62 are moved within a second range of motion beyond the first range of motion.

A person skilled in the art will appreciate that while FIGS. 1A-1C illustrate two flexible members 12, 14 and two connectors 16, 18, that any number of flexible members can be used. By way of non-limiting example, the implant 10 can include only one flexible member that is similar to flexible member 12 or 14. In another embodiment, shown in FIG. 4, the implant can include a single flexible member 13 that performs the function of flexible members 12 and 14. More particularly, the single flexible member 13 can have an hour-glass shape such that the narrow region of the hour glass extends between the spinous process of two adjacent vertebrae, and the widened ends of the hour glass extends at or adjacent to the location of the facet joints. This configuration is particularly useful in laminectomy procedures in which the spinous processes are removed. A person skilled in the art will also appreciate that the function of the flexible members 12, 14 and the connectors 16, 18 can be reversed. For example, the connectors 16, 18 can be formed from a flexible or deformable material, and members 12, 14 can be substantially rigid.

Each flexible member can have a variety of configurations, shapes, and sizes. In an exemplary embodiment, as shown, each flexible member 12, 14 has a generally elongate shape such that it is adapted to span across two or more adjacent vertebrae. While FIGS. 1A-1C illustrate substantially rectangular-shaped or oblong members 12, 14, in other exemplary embodiments the flexible members 12, 14 can have an oval shape, a cylindrical shape, etc. By way of non-limiting example, FIG. 2D illustrates two flexible members 12′, 14′ having an hour-glass shape. The length of the flexible members 12, 14 will vary depending on the number of levels being repaired and/or replaced, and thus the number of vertebrae to which the implant is to be attached to. As shown in FIGS. 1A-1C, each flexible member 12, 14 has a length that is adapted to span across two adjacent vertebrae 60, 62. The flexible members 12, 14 can also be adapted to be positioned on opposed sides of the spinous process, such that the flexible members 12, 14 can be positioned in or near the location of the facet joints, as is also shown in FIGS. 1A-1C.

Each flexible member 12, 14 also preferably includes at least one thru-bore formed therethrough for receiving the connectors 16, 18. As best shown in FIG. 1C, each flexible member 12, 14 includes a superior thru-bore 12 s, 14 s, and inferior thru-bore 12 i, 14 i. Each thru-bore 12 s, 12 i, 14 s, 14 i should have a size that is adapted to receive the connector 16, 18 therethrough preferably without allowing significant movement of the connector 16, 18 relative thereto, i.e., such that the connectors 16, 18 are in close contact with the thru-bores 12 s, 12 i, 14 s, 14 i. The thru-bores 12 s, 12 i, 14 s, 14 i are, however, preferably effective to allow at least one of the connectors 16, 18, and preferably both of the connectors 16, 18, to slide freely therethrough. Such a configuration allows the flexible members 12, 14 to slide along and/or rotate with respect to the connectors 16, 18, at least during a particular range of motion which will be discussed in more detail below.

Each thru-bore 12 s, 12 i, 14 s, 14 i can also be adapted to facilitate sliding and/or rotating movement of the flexible members 12, 14 relative to the connectors 16, 18. In an exemplary embodiment, the thru-bores 12 s, 12 i, 14 s, 14 i are preferably configured to prevent or reduce wearing thereof during use of the implant. While various techniques can be used to achieve this, in one exemplary embodiment each thru-bore 12 s, 12 i, 14 s, 14 i can include a bushing or bearing element disposed therein and adapted to slidably receive a connector 16, 18. In one exemplary embodiment, shown in FIG. 2C which illustrates flexible member 12, the superior thru-bore 12 s can include a superior bushing 20 s and the inferior thru-bore 12 i can include an inferior bushing 20 i. Each bushing 20 s, 20 i is in the form of a generally hollow, cylindrical member that is adapted to fit within the thru-bore 12 s, 12 i in the flexible member 12 and that functions as a bearing surface for the connectors 16, 18. The bushings 20 s, 20 i can, however, have virtually any shape and size.

In another embodiment (not shown), the flexible members 12, 14 can include a bearing surface formed within or integrally with the thru-bores 12 s, 12 i, 14 s, 14, and/or the thru-bores 12 s, 12 i, 14 s, 14 i can at least be modified to achieve properties that will facilitate movement of the connectors 16, 18 relative thereto. Alternatively, the thru-bores 12 s, 12 i, 14 s, 14 i, or at least a region surrounding the thru-bores 12 s, 12 i, 14 s, 14 i, can have a stiffness that is greater than a remainder of the flexible members 12, 14, or at least that is sufficient to minimize wear on the thru-bores 12 s, 12 i, 14 s, 14 i when the device 10 is implanted and in use. The bushings 20 s, 20 i, the thru-bores 12 s, 12 i, 14 s, 14 i, or bearing surface formed within the thru-bores 12 s, 12 i, 14 s, 14 i can be formed from any material. Suitable materials include, by way of non-limiting example, metals, ceramics, polymers, etc. A person skilled in the art will appreciate that a variety of techniques can be used to facilitate slidable and/or rotatable movement of the flexible members 12, 14 relative to the connectors 16, 18.

Each flexible member 12, 14 can also be formed from a variety of materials, but each flexible member 12, 14 is preferably effective to mimic the flexion/extension, rotation, lateral bending, and load carrying requirements of the posterior elements of the spine. In an exemplary embodiment, each flexible member 12, 14 is formed from a polymer, and more preferably a biocompatible polymer, such as polyurethane, composite reinforced polyurethane, silicone, etc. A person skilled in the art will appreciate that the material can vary depending on the intended use. For example, a material can be selected, based on a patient's size and condition, to have a particular stiffness.

The properties of the flexible members 12, 14 can also vary, and they can be uniform or non-uniform throughout the body thereof. In one embodiment, each flexible member 12, 14 can have a mid-portion 12 a, 14 a that is more elastic than terminal ends 12 b, 12 c, 14 b, 14 c of the flexible members 12, 14. The flexible members 12, 14 can also have regions that are more or less elastic than the remainder of the member 12, 14. In one exemplary embodiment, the flexible members 12, 14 can be configured to have a first elasticity during the first range of motion, and a second, different elasticity in a second range of motion beyond the first range of motion, as will be discussed in more detail below. In another exemplary embodiment, as noted above, the regions surrounding the thru-bores 12 s, 12 i, 14 s, 14 i can be formed from a material having a stiffness that is greater than the remainder of the flexible members 12, 14.

The connectors 16, 18 of the implant 10 can also have a variety of configurations, but in an exemplary embodiment they are adapted to allow the flexible members 12, 14 to slide and/or rotate freely, preferably without deforming, relative thereto when the superior and inferior vertebrae 60, 62 are moved within a first range of motion, and they are adapted to deform the flexible members 12, 14 when the superior and inferior vertebrae 60, 62 are moved within a second range of motion beyond the first range of motion. While various techniques can be used to achieve such a configuration, FIGS. 1A-1C illustrate one exemplary embodiment of superior and inferior connectors 16, 18.

The superior connector 16, which is shown in more detail in FIG. 2A, is preferably adapted to couple to opposed pedicles 60 a, 60 b (FIG. 1A) of the superior vertebra 60 and to extend between the pedicles 60 a, 60 b and inferior to the spinous process 60 s. The configuration of the superior connector 16 can, however, change where a laminectomy is performed and the spinous process 60 s has been removed. The connector 16 can, for example, be substantially linear. In the embodiment shown in FIG. 2A, the superior connector 16 is in the form of a substantially v-shaped rod and it preferably includes a central linear portion 16 a with two lateral arms 16 b, 16 c extending at an angle α relative to the central portion 16 a. The angle α can vary depending on the size of the patient, and in particular depending on the distance between the opposed pedicles 60 a, 60 b and the angle necessary to allow the superior connector 16 to extend around the spinous process 60 s. The angle α is also determinative of the range of sliding motion between the flexible members 12, 14 and the connectors 16, 18. In particular, the range of motion of the flexible members 12, 14 along the connectors 16, 18 will increase as the angle increases. This will be discussed in more detail below. While the angle α can vary, in an exemplary embodiment, the angle α is in the range of about 95° to 180°.

The inferior connector 18, which is shown in more detail in FIG. 2B, is similarly adapted to couple to the opposed pedicles 62 a, 62 b (FIG. 1A) of the inferior vertebra 62 and to extend between the pedicles 62 a, 62 b ands superior to the spinous process 62 s. The connector 18, however, preferably has a substantially linear configuration. In an exemplary embodiment, as shown in FIG. 2B, the connector 18 is in the form of a rod having a v-shaped portion 18 a formed therein, preferably at a substantially central portion thereof. The v-shaped portion 18 a is configured to extend around, and be positioned superior to the spinous process 62 s of the vertebra 60.

Each connector 16, 18 can also be formed from a variety of materials, but preferably the connectors 16, 18 are substantially rigid. In an exemplary embodiment, the connectors 16, 18 are formed from a bioimplantable metal, such as titanium, stainless steel, and cobalt and nickel based alloys, such as cobalt-chromium-molybdenum (Co—Cr Mo).

In use, the implant 10 can be used to replace one or more of the posterior elements of the spine, including, for example, the facet joints, the lamina, the posterior ligaments, and/or other features of a patient's spinal column. The implant 10 can also be adapted to function with either a natural vertebral disc, or with an artificial disc. Regardless, as noted above, the implant 10 is preferably adapted to mimic the function of the posterior elements, without necessarily mimicking the anatomy. The device 10 is implanted by first positioning the superior and inferior connectors 16, 18 through the thru-bores 12 s, 12 i, 14 s, 14 i in the flexible members 12, 14. If necessary, other procedures, such as a facetectomy and/or laminectomy, can be performed. The terminal ends 16 t ₁, 16 t ₂, 18 t ₁, 18 t ₂ of the connectors 16, 18 are then attached to the superior and inferior vertebrae 60, 62. As noted above, the superior connector 16 is preferably attached to the opposed pedicles 60 a, 60 b on the superior vertebra 60, and the inferior connector 18 is preferably attached to the opposed pedicles 62 a, 62 b on the inferior vertebra 62.

The connectors 16, 18 can be attached to the vertebrae 60, 62 using a variety of anchoring devices and other techniques known in the art. In an exemplary embodiment, as shown in FIGS. 1A-1C, the connectors 16, 18 are attached to the vertebrae 60, 62 using spinal anchors, and in particular spinal screws. While only a portion of the spinal screws are shown, each screw includes a rod-receiving head 70, 72, 74, 76 that is configured to seat a terminal end 16 t ₁, 16 t ₂, 18 t ₁, 18 t ₂ of a connector 16, 18. A fastening element, such as a set screw, can be used to lock the connectors 16, 18 to the screws 70, 72, 74, 76.

While not shown, several additional connectors can be attached to adjacent vertebrae and positioned to extend through flexible members 16, 18, or through separate flexible members, thereby forming a multi-level replacement. The number of connectors, and optionally the number of flexible members, will vary depending on the number of levels being repaired. In attaching additional connectors, each pair of spinal anchors, e.g., spinal screws 70, 72, 74, 76, can be configured to mate to two connectors. Thus, for example, if a third vertebra, located inferior to the second vertebra 62, were coupled to the first and second vertebra 60, 62, a superior connector would mate to spinal anchors 74, 76, and an inferior connector would mate to spinal anchors disposed within the pedicles of the third vertebra. This procedure could be repeated for multiple vertebrae. While not shown, the procedure can also include the step of placing a sheath or protective member partially or fully around the implant 10 for preventing tissue from growing on the implant 10 and into the thru-bores 12 s, 12 i, 14 s, 14 i, and for preventing debris from migrating into the spinal canal.

Once the connectors 16, 18 are fixedly attached to the vertebrae 60, 62, the implant 10 is effective to control movement of the vertebrae relative to one another. More particularly, the implant 10 is effective to mimic the natural function of the spine. FIG. 3 is a chart illustrating the load-deformation curve of a functional spine unit (FSU). As shown, the FSU is highly flexible at low loads, and it stiffens as the load increases. Thus, the FSU becomes much less flexible as the range of motion increases. To analyze this nonlinear biphasic behavior, the load-displacement curve is divided into two parts: (1) the neutral zone, in which the FSU is highly flexible, and (2) the elastic zone, in which the FSU is much less flexible, and has a high degree of stiffness. The two zones together constitute the physiological range of motion of a zone. The implant 10 is adapted to mimic this behavior. In particular, during flexion of the vertebrae 60, 62 relative to one another in the neutral zone, referred to herein as the first range of motion, the flexible members 12, 14 are free to slide along and/or rotate with respect to the connectors 16, 18. Thus, as the vertebrae flex away from one another, while in the neutral zone, the connectors 16, 18 are moved apart from one another thereby causing the flexible members 12, 14 to move toward one another. Similarly, during extension, the flexible members 12, 14 are free to slide and/or rotate, however they will move apart from one another. Such movement is at least in part due to the shape of the connectors 16, 1, and in particular the v-shape of the superior connector 16. When the vertebrae 60, 62 are further flexed relative to one another in the elastic zone, referred to herein as the second range of motion (which is necessarily beyond than the first range of motion), the flexible members 12, 14 are forced to deform, which can include stretching, rotating, etc. This is a result of the shape of the connectors 16, 18, which prevent the flexible members 12, 14 from moving further toward one another. As a result, in the first range of motion, the implant 10 mimics the natural spine by allowing a greater degree of flexibility, as the connectors 16, 18 allow the flexible members 12, 14 to slide therealong and/or rotate relative thereto with minimal resistance, and in the second range of motion, the implant 10 mimics the natural spine by controlling flexibility, as the connectors 16, 18 cause the flexible members 12, 14 to deform, thereby resisting flexion. As discussed above, the properties of the flexible members 12, 14 will necessarily affect the resistance to flexion, and the flexible members 12, 14 can be especially adapted to have a first flexibility in the first range of motion and a second flexibility in the second range of motion. Since each patient's specific needs will vary, the implant 10 can be provided as part of a kit having several flexible members 12, 14 varying in shape, size, and stiffness. The flexible members 12, 14 can also be particularly tailored to different levels of a patient's spine.

The implant can also optionally include physical stops to control when the flexible members stop sliding and/or rotating and are forced to deform. In particular, the physical stops can be formed on or attached to the connectors 16, 18 at a location that will prevent the flexible members 12, 14 from sliding and/or rotating at a particular point during flexion of the vertebrae. By way of non-limiting example, FIG. 2D illustrates outer stops 12 x′, 14 x′ disposed on the superior connector 16′ on opposed sides of the flexible members 12′, 14′. A central stop 16 x′ is also formed on the connector 16′ between the flexible members 12′, 14′. The outer stops 12 x′, 14 x′ are in the form of band clamps which can be adjustably positioned at various locations along the connector 16′. The central stop 16 x′ is in the formed of a stepped member, and it can also optionally be adjustable. For example, the central stop 16 x′ can be in the form of a housing and the opposed sides of the connector 16′ can thread into the housing. A person skilled in the art will appreciate that the stops can have any configuration and that a variety of other techniques can be used to control movement between the vertebrae in such a manner that mimics the natural function of the spine.

One skilled in the art will appreciate further features and advantages of the invention based on the above-described embodiments. Accordingly, the invention is not to be limited by what has been particularly shown and described, except as indicated by the appended claims. All publications and references cited herein are expressly incorporated herein by reference in their entirety. 

1. An implantable device for stabilizing the spine, comprising: at least one flexible member adapted to span across at least two adjacent vertebrae in a patient's spinal column; a superior connector adapted to be coupled to a superior vertebra and an inferior connector adapted to be coupled to an inferior vertebra, the superior and inferior connectors extending through the at least one flexible member such that the superior and inferior connectors and the at least one flexible member are effective to control movement between the superior and inferior vertebrae.
 2. The implantable device of claim 1, wherein the superior connector is movable relative to the at least one flexible member.
 3. The implantable device of claim 1, further comprising first and second flexible members.
 4. The implantable device of claim 1, wherein each flexible member includes at least two thru-bores formed therein for receiving the superior and inferior connectors therethrough.
 5. The implantable device of claim 4, wherein each thru-bore includes a bushing disposed therein and adapted to receive a connector therethrough.
 6. The implantable device of claim 4, wherein each thru-bore includes a bearing formed therein and adapted to receive a connector therethrough.
 7. The implantable device of claim 4, wherein a region surrounding each thru-bore is adapted to provide stability to the connector extending therethrough.
 8. The implantable device of claim 7, wherein each region is substantially rigid.
 9. The implantable device of claim 1, wherein each connector comprises a substantially rigid rod.
 10. The implantable device of claim 1, wherein the superior connector includes opposed terminal ends that are adapted to be coupled to pedicles of a superior vertebra, and a mid-portion that is adapted to extend around and be positioned inferior to a spinous process of a superior vertebra, and wherein the inferior connector includes opposed terminal ends that are adapted to be coupled to pedicles of an inferior vertebra, and a mid-portion that is adapted to be positioned proximate and superior to a spinous process of an inferior vertebra.
 11. The implantable device of claim 10, wherein the superior connector is substantially v-shaped and the inferior connector is generally linear with a v-shaped portion formed therein.
 12. The implantable device of claim 11, wherein the v-shaped portion in the inferior connector is formed at a substantial mid-point thereof.
 13. The implantable device of claim 12, wherein the v-shaped portion in the inferior connector is adapted to fit around a spinous process of an inferior vertebra.
 14. The implantable device of claim 11, wherein the v-shaped superior connector includes a central linear portion and first and second lateral arms extending at an angle relative to the central linear portion.
 15. The implantable device of claim 1, wherein each connector includes first and second terminal ends adapted to be fixedly mated to opposed sides of a vertebra.
 16. The implantable device of claim 15, further comprising a plurality of spinal anchors, each being adapted to be implanted in a vertebra and to fixedly mate a terminal end of a connector to the vertebra.
 17. The implantable device of claim 16, wherein each spinal anchor comprises a spinal screw having a rod-receiving head formed thereon, and wherein each connector comprises a rod.
 18. The implantable device of claim 1, wherein the at least one flexible member is formed from a material selected from the group consisting of polyurethane, composite reinforced polyurethane, and silicones.
 19. The implantable device of claim 1, wherein the at least one flexible member comprises a single flexible member having a substantially hour-glass shape.
 20. The implantable device of claim 1, wherein the at least one flexible member has a central portion that has an elasticity that is greater than an elasticity of opposed superior and inferior terminal ends thereof.
 21. An implantable device for stabilizing the spine, comprising: first and second dynamic stabilizing members adapted to be positioned adjacent to opposed sides of a spinous process and to extend along at least two adjacent vertebrae in a patient's spinal column; and at least one pair of stabilizing rods adapted to extend through the first and second dynamic stabilizing members and to couple to two adjacent vertebrae to control movement between the adjacent vertebrae.
 22. The implantable device of claim 21, wherein the first and second dynamic stabilizing members are substantially flexible.
 23. The implantable device of claim 22, wherein the first and second dynamic stabilizing members each have a flexibility that varies along a length thereof.
 24. The implantable device of claim 22, wherein the first and second dynamic stabilizing members each have a mid-portion having a flexibility that is greater than a flexibility of opposed terminal ends thereof.
 25. The implantable device of claim 21, wherein a pair of stabilizing rods comprises a superior stabilizing rod and an inferior stabilizing rod, and wherein the first and second dynamic stabilizing members each include a superior hole formed therein and adapted to receive the superior stabilizing rod, and an inferior hole formed therein and adapted to receive the inferior stabilizing rod.
 26. The implantable device of claim 25, wherein the superior stabilizing member includes opposed terminal ends that are adapted to be coupled to pedicles of a vertebra, and a mid-portion that is adapted to extend around and be positioned inferior to a spinous process of a vertebra.
 27. The implantable device of claim 25, wherein the inferior stabilizing member includes opposed terminal ends that are adapted to be coupled to pedicles of an inferior vertebra, and a mid-portion that is adapted to be positioned proximate and inferior to a spinous process of an adjacent superior vertebra.
 28. The implantable device of claim 25, wherein the superior stabilizing member has a generally elongate shape with a v-shaped portion formed therein, and wherein the inferior stabilizing member is substantially v-shaped.
 29. The implantable device of claim 25, wherein the superior and inferior holes in the first and second dynamic stabilizing members each include a bearing element disposed therein and adapted to receive the stabilizing rod.
 30. The implantable device of claim 25, wherein the superior and inferior holes in the first and second dynamic stabilizing members are adapted to rigidly support the stabilizing rod relative to the dynamic stabilizing member.
 31. The implantable device of claim 30, wherein a region surrounding the superior and inferior holes in the first and second dynamic stabilizing members have an elasticity that is less than an elasticity of the remainder of the first and second dynamic stabilizing members.
 32. A posterior element replacement implant, comprising: at least one flexible member; and at least one connector adapted to be coupled to adjacent vertebrae and adapted to extend through the at least one flexible member; wherein the at least one connector is adapted to move relative to the at least one flexible member without substantially deforming the at least one flexible member when the adjacent vertebrae are moved within a first range of motion, and wherein the at least one connector is adapted to deform the at least one flexible member when the adjacent vertebrae are moved within a second range of motion beyond the first range of motion.
 33. The implant of claim 32, wherein the at least one connector comprises a superior connector and an inferior connector.
 34. The implant of claim 33, wherein the superior and inferior connectors each comprise a substantially rigid rod.
 35. The implant of claim 34, wherein the superior rod is substantially v-shaped, and the inferior rod is substantially linear with a v-shaped portion formed therein.
 36. The implant of claim 33, wherein the at least one flexible member comprises first and second flexible members.
 37. The implant of claim 36, wherein the first and second flexible members each have a substantially elongate shape with first and second thru-bores formed therein for receiving the superior and inferior connectors.
 38. The implant of claim 37, wherein each thru-bore includes a bearing formed therein and adapted to receive a connector extending therethrough.
 39. An implantable posterior element repair kit, comprising: a plurality of pairs of dynamic stabilizing members, each pair comprising first and second dynamic stabilizing members adapted to be positioned adjacent to opposed sides of a spinous process and to extend along at least two adjacent vertebrae in a patient's spinal column; and a plurality of pairs of stabilizing rods, each pair of stabilizing rods being adapted to couple to a pair of dynamic stabilizing members and to couple to two adjacent vertebrae to control movement between the adjacent vertebrae.
 40. The kit of claim 39, wherein each of the plurality of pairs of dynamic stabilizing members has an elasticity that differs from one another.
 41. The kit of claim 39, wherein each of the plurality of pairs of dynamic stabilizing members has a size that differs from one another.
 42. The kit of claim 39, wherein each of the plurality of pairs of dynamic stabilizing members has a shape that differs from one another.
 43. A method for stabilizing the posterior element in adjacent vertebrae, comprising: coupling at least one flexible member to two adjacent vertebrae with at least one connector such that the at least one connector is movable relative to the at least one flexible member without substantially deforming the at least one flexible member when the vertebrae are moved within a first range of motion, and such that the at least one connector is effective to deform the at least one flexible member when the vertebrae are moved within a second range of motion beyond the first range of motion.
 44. The method of claim 43, wherein the step of coupling at least flexible member to two adjacent vertebrae with at least one connector comprises coupling a superior connector to a superior vertebra, the superior connector extending through first and second flexible members, and coupling an inferior connector to an inferior vertebra, the inferior connector extending through the first and second flexible members.
 45. The method of claim 44, wherein the step of coupling the superior connector to the superior vertebra comprises implanting first and second spinal anchors in the superior vertebra and locking the superior connector to the first and second spinal anchors, and wherein the step of coupling the inferior connector to the inferior vertebra comprises implanting first and second spinal anchors in the inferior vertebra and locking the inferior connector to the first and second spinal anchors.
 46. A method for mimicking the normal function of adjacent vertebrae in a patient's spinal column, comprising: implanting a first pair of spinal anchors in opposed pedicles of a first vertebra, and implanting a second pair of spinal anchors in opposed pedicles of an adjacent second vertebra; coupling opposed terminal ends of a first rigid member to the first pair of spinal anchors in the first vertebra, and coupling opposed terminal ends of a second rigid member to the second pair of spinal anchors in the second vertebra, the first and second rigid members extending through at least one flexible member.
 47. The method of claim 46, wherein the at least one flexible member comprises first and second flexible members positioned on opposed sides of a spinous process of each vertebra.
 48. The method of claim 46, wherein the first rigid member is substantially v-shaped, and the second rigid member is substantially linear with a v-shaped portion formed therein.
 49. The method of claim 46, wherein the first rigid member extends from the opposed pedicles inferior to a spinous process of the first vertebra, and wherein the second rigid member extends from the opposed pedicles superior to a spinous process of the second vertebra.
 50. The method of claim 46, wherein each spinal anchor comprises a spinal screw having a receiver head formed thereon and adapted to seat a terminal end of a rigid member.
 51. The method of claim 46, further comprising the steps of implanting a third pair of spinal anchors in opposed pedicles of a third vertebra adjacent to the second vertebra, coupling opposed terminal ends of a third rigid member to the second pair of spinal anchors in the second vertebra, and coupling opposed terminal ends of a fourth rigid member to the third pair of spinal anchors in the third vertebra, the third and fourth rigid members extending through the at least one flexible member.
 52. A method for providing stability to adjacent vertebrae, comprising coupling a superior stabilizing rod to opposed sides of a superior vertebra and coupling an inferior stabilizing rod to opposed sides of an inferior vertebra such that movement between the superior and inferior vertebrae is controlled by at least one flexible member coupled to each of the superior and inferior stabilizing rods.
 53. The method of claim 52, wherein the superior stabilizing rod is adapted to move relative to the at least one flexible member without substantially deforming the at least one flexible when the superior and inferior vertebrae are moved relative to one another within a first range of motion, and wherein the superior stabilizing rod is adapted to deform the at least one flexible member when the superior and inferior vertebrae are moved relative to one another within a second range of motion beyond the first range of motion.
 54. A spinal stabilization device, comprising: a first elongate connector adapted to couple to opposed lateral sides of a first vertebra; a second elongate connector adapted to couple to opposed lateral sides of a second vertebra adjacent to the first vertebra; and at least one flexible member movably coupled to the first and second elongate connectors such that, when the connectors are mated to adjacent first and second vertebrae, the connectors and the at least one flexible member are effective to allow controlled movement of the adjacent first and second vertebrae. 